The present invention relates to a compact disk ROM (hereinafter, referred to as CD ROM) decoder, and more particularly, to a descrambling data generating circuit, the method thereof, and a descrambler.
In general, transmitted synchronous data having successive values of "0" or "1", might not be capable of proper synchronization by a receiver. To overcome this, a transmitter randomizes transmitted data using a scrambler. The receiver uses a descrambler to convert the received data into the original data. The scrambler divides the transmitted data by a constant polynomial. In turn, the descrambler multiplies the scrambled data by the constant polynomial converting the scrambled data into to the original data.
A compact disk digital audio (CD-DA) recording system employ scrambling to reduce the probability of generating the same sync signal pattern inserted into audio data. In the same manner, a CD ROM decoder performs a descrambling process in order to convert the scrambled data into the original data. The scrambled data is comprised of 2352 byte blocks that each include 12-bytes of sync data.
FIG. 1 is a block diagram of a CD ROM decoder, peripheral devices, and more particularly the position occupied by a descrambler in the CD system.
FIG. 2 is a block diagram of a conventional descrambler. Reference numerals 21, 23, 25, and 27 denote a descrambling data generator, a serial-parallel (S/P) converter, a data ordering unit and a sync detector, respectively. Reference numerals 29, 30, 31 and 33 denote a parallel-serial (P/S) converter, an exclusive-OR (EX-OR) gate, a S/P converter and an L-R separator, respectively.
The descrambling data generator 21 generates descrambling data (DSCR) according to a polynomial [p(x)=X.sup.15 +X+1], and includes 15 serially connected flip-flops (F1-F15) and an EX-OR gate 22. The 15 flip-flops commonly receive a clock signal CLK via a clock terminal. The EX-OR gate 22 performs an EX-OR operation with respect to the output signals of the 14th and 15th flip-flops F14 and F15, and applies the result to an input terminal of the first flip-flop F1. The initial value of the descrambling data generator 21 is "000000000000001".
The S/P converter 23 converts serial data (SIDATA) input from a compact disk player (FIG. 1) into 16-bit parallel data. The data ordering unit 25 determines a data format according to a control signal (LMSEL) input from the compact disk player. The sync detector 27 detects sync signals from the data output from the data ordering unit 25. The sync signals include sync start, sync detect and sync end signals. The P/S converter 29 converts the 16-bit signals output from the data ordering unit 25 into one bit serial data.
The EX-OR gate 30 performs an exclusive OR operation with the output data DSCR of the descrambling data generator 21 and the output data of the P/S converter 29. The S/P converter 31 converts the one-bit serial data output from the EX-OR gate 30 into 16-bit parallel data. The L-R separator 33 separates the 16-bit data output from the S/P converter 31 into 8-bit L-channel data and 8-bit R-channel data that is then alternately output.
As described above, the S/P converter 23 in the conventional descrambler converts the one-bit serial data (SIDATA) into 16-bit parallel data. The converted 16-bit data is then converted back into one-bit serial data with the P/S converter 29. This is because the descrambling data generator 21 outputs the descrambling data DSCR in one bit units. Having passed through the EX-OR gate 30, the one-bit data is converted into parallel data by the S/P converter 31. The conventional descrambler is slow due to the repeated serial-parallel conversions.
To solve the aforementioned problem, an object of the present invention is to provide a simplified descrambling data generating circuit for a CD ROM decoder which is capable of operating at high speeds.
The second object of the present invention is to provide a simple method for generating descrambling data in a CD ROM decoder.
Another object of the present invention is to provide a descrambler for a CD ROM decoder that uses the improved descrambling data generating circuit and method of the invention.